Considering a new alignment for 8x LMS 5400 Ultra 18s. Thoughts? - AVS Forum
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post #1 of 185 Old 11-29-2013, 08:04 PM - Thread Starter
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So, I've been concerned about xmax with low frequency signals around 17-20hz at high levels. Often times if I'm pushing too far the cones in my subs will tap the spiders. I've been looking around at other drivers and nothing at the moment is really catching my interest. The talk of a 24 with a strong motor definitely caught my attention, but who knows if and when this will ever materialize. I'm open to any suggestions.

Here is what I've been modeling. Using the same drivers and amps. This is with a 10 cube box tuned to 15hz. Using a 4th order butterworth filter at 13hz to control excursion. This is modeled with 3kw into the vented enclosure and 4kw into the sealed.

SPL


Excursion:


And multiplied by 8 SPL:
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post #2 of 185 Old 11-29-2013, 09:14 PM
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I know what I'd be doing!
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post #3 of 185 Old 11-29-2013, 09:15 PM
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Looking at your theater, it's a tight fit horizontally but you've got room vertically. There is thread for a Gjallarhorn refold. The dimensions are like 25"wide 32"deep 72" tall. Maybe LTD02 could modify it to be around 20"wide and make use of the available height so you could fit 4? One Gjallarhorn is reported to equal 4 sealed LMS down low, obviously not below tuning. I think that is one possibility.
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post #4 of 185 Old 11-29-2013, 09:26 PM - Thread Starter
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Originally Posted by gpmbc View Post

Looking at your theater, it's a tight fit horizontally but you've got room vertically. There is thread for a Gjallarhorn refold. The dimensions are like 25"wide 32"deep 72" tall. Maybe LTD02 could modify it to be around 20"wide and make use of the available height so you could fit 4? One Gjallarhorn is reported to equal 4 sealed LMS down low, obviously not below tuning. I think that is one possibility.

Building 8 of those would be too much. I don't have that kind of time. Those are fairly complicated horn builds. Building 4 enclosures is doable. Modeling says I'll gain 9db at 17hz and lose nothing above 10hz. It is interesting, and I thought about it a bit.... just the size/time limitations prevented me from going any further.

I figure 4 dual opposed boxes will do the job. I was also considering some kind of stackable units ala Bosso.
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post #5 of 185 Old 11-29-2013, 09:29 PM
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Building 8 of those would be too much. I don't have that kind of time. Those are fairly complicated horn builds. Building 4 enclosures is doable. Modeling says I'll gain 9db at 17hz and lose nothing above 10hz. It is interesting, and I thought about it a bit.... just the size/time limitations prevented me from going any furhter.

Yeah man, 4 would blow your socks off.

If you can find someone to CNC the pieces it wouldn't be that bad.
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post #6 of 185 Old 11-29-2013, 09:40 PM
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The 15hz vented looks like a monster too. Is that what you were referring to for dual opposed?
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post #7 of 185 Old 11-29-2013, 09:46 PM - Thread Starter
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The 15hz vented looks like a monster too. Is that what you were referring to for dual opposed?

Yes. If I decide to go that way, it will be challenging coming up with a design I like. I don't want to end up firing these into my walls. Once I get some time I'll brainstorm some ideas and see what I can fit in my space.

I may also just end up building 8 smaller cabs and stacking them. No clue yet.
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post #8 of 185 Old 11-29-2013, 09:52 PM
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Another thing to mention about the Ghorns is that you don't want to run them over 60hz due to ringing. The first spike in response is 63hz.

However, if you build 4 of them, you'd still have 4 LMS's and 2 clones to work out something to augment the mid-bass with...
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post #9 of 185 Old 11-29-2013, 11:16 PM
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Are you looking to gain output or only minimize your excursion issues? Are you willing to have a cut off around 10-15Hz instead of going to 5-7Hz with your current sealed subs?
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post #10 of 185 Old 11-29-2013, 11:34 PM
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"Here is what I've been modeling. Using the same drivers and amps. This is with a 10 cube box tuned to 15hz. Using a 4th order butterworth filter at 13hz to control excursion. This is modeled with 3kw into the vented enclosure and 4kw into the sealed."

'not is building martysubs? lol...actually, i think that is a good way to up the spl while keeping cone excursion down without getting into some other issues unless you want to go "giant" with a low tuned front loaded super horn.

a simple way to get there is an upward firing rear slot port with multiple front firing drivers.

here is a mockup of quad front firing: http://www.avsforum.com/t/1494429/help-with-speaker-subwoofer-design/60#post_23834121

such could be run vertically or stacked horizontally with ports firing in opposite directions if that turns out to matter at all. essentially the same form factor that you have currently, just scaled up a bit. :-)


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post #11 of 185 Old 11-29-2013, 11:44 PM
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"Building 8 of those would be too much. I don't have that kind of time. Those are fairly complicated horn builds."

and just an fyi...we are actually ironing out wrinkles right now on the gh refold, so there may be one up and running shortly.

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post #12 of 185 Old 11-29-2013, 11:45 PM - Thread Starter
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Quote:
Originally Posted by Decadent_Spectre View Post

Are you looking to gain output or only minimize your excursion issues? Are you willing to have a cut off around 10-15Hz instead of going to 5-7Hz with your current sealed subs?

Well what I've modeled will reduce excursion and gain output and put my -3db point to 9hz instead of 7hz... so I think it's a win. Just need to decide on enclosures mostly at this point if I go that route...
Quote:
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"Here is what I've been modeling. Using the same drivers and amps. This is with a 10 cube box tuned to 15hz. Using a 4th order butterworth filter at 13hz to control excursion. This is modeled with 3kw into the vented enclosure and 4kw into the sealed."

'not is building martysubs? lol...actually, i think that is a good way to up the spl while keeping cone excursion down without getting into some other issues unless you want to go "giant" with a low tuned front loaded super horn.

a simple way to get there is an upward firing rear slot port with multiple front firing drivers.

here is a mockup of quad front firing: http://www.avsforum.com/t/1494429/help-with-speaker-subwoofer-design/60#post_23834121

such could be run vertically or stacked horizontally with ports firing in opposite directions if that turns out to matter at all. essentially the same form factor that you have currently, just scaled up a bit. :-)


I was thinking of doing something like this except with the ports facing forward possibly on top of the enclosure or the side. I'd keep the woofers as low as possible so the enclosure would be stable.

What are your thoughts on spacing the woofers further apart or packing them closer together?
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post #13 of 185 Old 11-29-2013, 11:50 PM - Thread Starter
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I was also thinking of doing something dual opposed with drivers firing vertically. Not sure if that would cause any issues with them far apart.
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post #14 of 185 Old 11-29-2013, 11:51 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

"Building 8 of those would be too much. I don't have that kind of time. Those are fairly complicated horn builds."

and just an fyi...we are actually ironing out wrinkles right now on the gh refold, so there may be one up and running shortly.

Too big and too much work, want extension to 10hz and don't want to have limited bandwidth up top either.
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post #15 of 185 Old 11-30-2013, 12:01 AM
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as long as they are within 1/4 wavelength, they will combine into a single source (at least in some sense)...but the other approach is all that talk about 1/4 distances to kill room modes and that would call for fairly wide spacing. one consideration there is vibration of the driver near the top of the enclosure, as you pointed out, so extra care would be required to make that work. not sure with so many sources if side/height modes are a problem for you or not.

just for fun, imax had a sub that used 4 x lab12's iirc. one box. ported. scaling something like that up for what you are talking about might not be possible, but with two of the drivers 'magnets out' and about 40 cubic feet or so at work, it might be one of meanest subs going...

this is my interpretation which is the imax with labs, but with two "magnets out."


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post #16 of 185 Old 11-30-2013, 12:05 AM - Thread Starter
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Hm, interesting. I think that'd work better with something like the lab12, and not so much an lms ultra which are ~90lbs each wink.gif That's a lot of magnet to hang outside of the box. If I do 4 per box I'd need ~40cuft boxes.... gears are turning... might be nice, but there's the issue of moving them later as it will likely weigh over 400lbs.
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post #17 of 185 Old 11-30-2013, 12:08 AM
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You need to pick a compromise somewhere, you want to gain output and reduce excursion, for this you are willing to trade some extension but you also need a larger box, your options are basically a FLH/TH or a ported cab. The question at this point is what box size is acceptable, and how much bandwidth.

Personally I would avoid the GH unless you use it for only below 40Hz due to time domain issues, the ported box will be simplest to build and a FLH will be the optimum choice if you have space and can outsource construction. I feel that for your situation a ported cab is probably the right choice as a powerful 10Hz FLH is going to be large.
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post #18 of 185 Old 11-30-2013, 12:09 AM
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post #19 of 185 Old 11-30-2013, 12:11 AM - Thread Starter
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When I build the new boxes, I'll have to make sure to mount all the logos straight this time wink.gif
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post #20 of 185 Old 11-30-2013, 12:34 AM
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Reminds me of a 4 driver Captivator.
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post #21 of 185 Old 11-30-2013, 12:53 AM - Thread Starter
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I'm having trouble with the porting. Seems any resonance that's high enough also comes along with high air velocities.
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post #22 of 185 Old 11-30-2013, 01:01 AM
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What's the thought of going with passive radiators on this one? Sounds like it would solve most of the issues wrt the port/vent.

My Dual 18" LLT subs 120dB down to 10hz

 

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post #23 of 185 Old 11-30-2013, 01:02 AM - Thread Starter
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What's the thought of going with passive radiators on this one? Sounds like it would solve most of the issues wrt the port/vent.

More expense, would rather avoid if possible.
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post #24 of 185 Old 11-30-2013, 01:04 AM
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More expense, would rather avoid if possible.

Right. That would be the downside on that one. wink.gif

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post #25 of 185 Old 11-30-2013, 01:28 AM - Thread Starter
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Right. That would be the downside on that one. wink.gif

Also, seems the output for a PR is lower than a port below tuning freq.
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post #26 of 185 Old 11-30-2013, 01:38 AM
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My models looks fine. I made the overall volume higher than you might have liked. ~7cuft per driver and with 4kw input and using two PR's of AE PR18 equivalent performance run out of excursion around 20hz. Hmph. Tune is just under 16hz though. Mighty beastly output too.

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post #27 of 185 Old 11-30-2013, 01:49 AM - Thread Starter
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My models looks fine. I made the overall volume higher than you might have liked. ~7cuft per driver and with 4kw input and using two PR's of AE PR18 equivalent performance run out of excursion around 20hz. Hmph. Tune is just under 16hz though. Mighty beastly output too.

post em? Using the AE PR's it's down quite a few db compared to the ported config.
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post #28 of 185 Old 11-30-2013, 01:50 AM - Thread Starter
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Maybe I'll just match the port resonant frequency to the null @ the LP smile.gif
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post #29 of 185 Old 11-30-2013, 01:55 AM
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post em? Using the AE PR's it's down quite a few db compared to the ported config.

I got this model using 4kw input and using two AE PR18's at max weight rating. With a roughly 7cuft space I get a tune of 15.9hz. Sure looks nice if you don' care about output/extension <15hz which.... I could understand. tongue.gif



Now multiply by eight. eek.gif

That's all I've got for now. Time for Scooter to hit the hay. smile.gif

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post #30 of 185 Old 11-30-2013, 02:02 AM - Thread Starter
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That's pretty nice, but according to my sims it's pushing the PRs beyond xmax. I'd also need 16 of them, which is about $2000.

Not sure which way to go from here. I'll have to sleep on it.

What's the acceptable limits of air velocity in a slot port in something like this before the port a) stops giving benefits and b) makes too much noise?

With a port resonance around 120hz I'm seeing air speeds around 30m/s at peak.
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